CD59 and paroxysmal nocturnal hemoglobinuria: We evaluated the role of properdin in an in vitro model of PNH that we previously developed (24), where an inhibitory anti-CD59 MoAb was added to the EH, and rH19-20 was added to amplify the sensitivity of the assay because inhibiting CD59 alone only allows a maximum of 20% lysis (24).